Sizing and Licensing AS RT PO, OS RT PO, and SEC Capacity for Redundant Fail-Safe S7-400H Systems

In SIMATIC PCS 7, calculating licenses for a redundant CPU 410-5H system with 500 redundant fail-safe digital inputs and 500 outputs requires separating software runtime licenses from Process Object (PO) counts. Pure fail-safe channel drivers (F_CH_DI, F_CH_DO) and safety logic blocks consume zero AS RT POs and zero OS RT POs. S7 F Systems requires one S7 F Systems Runtime license per active CPU (two licenses for a 410H redundant pair). Process Objects are consumed only if safety signals interconnect with standard APL blocks (such as MonDiL or MotL) for OS visualization: each technological block consumes one AS RT PO and one OS RT PO. Each CPU 410-5H requires an identical System Expansion Card (SEC) sized to cover the AS PO total. Validate license quantities with an authorized Siemens distributor or the Siemens Industry Mall.

Executive Summary

When designing high-availability emergency shutdown (ESD) or burner management systems (BMS) in SIMATIC PCS 7 V9.0, system engineers frequently struggle to calculate licensing requirements for large fail-safe I/O counts (such as 500 redundant F-DI and 500 redundant F-DO channels on a CPU 410-5H pair). A common costly mistake is assuming every physical fail-safe I/O channel consumes an AS Process Object (PO) and OS Process Object. In reality, Siemens safety channel drivers do not consume PO licenses. This technical guide outlines the precise calculation rules for S7 F Systems RT licenses, AS RT POs, OS RT POs, and CPU 410 System Expansion Card (SEC) capacity.

Architecture and Fundamental Mechanics

The licensing architecture of SIMATIC PCS 7 divides safety execution, controller capacity, and operator visualization into independent accounting domains:
1. S7 F Systems Runtime Licensing:
Executing fail-safe F-blocks (from the S7 F Systems Lib) inside safety-instrumented shutdown groups requires the S7 F Systems Runtime License. In a redundant S7-400H / CPU 410-5H system, each physical CPU executes safety logic; therefore, two S7 F Systems Runtime licenses are required (one per controller).
2. Process Object (AS RT PO) Rules for Safety Channels:
- Pure Safety Channels: Fail-safe channel drivers (F_CH_DI, F_CH_DO, F_CH_AI) and mathematical/logical safety gates (F_AND4, F_OR4, Safety Matrix) operate inside the safety program. They consume 0 AS Process Objects.
- Technological Visualization: An AS RT PO is deducted only when an APL block (such as MonDiL FB1848, MotL FB1850, or VlvL FB1899) is instantiated to transmit status to WinCC. If 200 of the 500 inputs are visualized via MonDiL, exactly 200 AS POs are consumed.
3. OS Runtime Process Objects (OS RT PO):
WinCC OS licensing counts technological blocks that have operator control, faceplates, or message generation (S7_m_c := 'true'). If 200 blocks communicate with the OS Single Station, a 250 OS RT PO license package is required.
4. CPU 410-5H System Expansion Card (SEC) Hardware Licensing:
The CPU 410-5H hardware capacity is locked to its plugged-in System Expansion Card (SEC). The SEC must be sized to cover the total AS PO demand (available in tiers: 100, 500, 1000, 1600, 2000+ POs). In redundant configurations, both CPUs must have identical SEC cards.

Step-by-Step Implementation Procedure

Determine Pure Safety vs Visualized I/O Allocation:
a. Itemize all 500 F-DI and 500 F-DO channels in the equipment schedule.
b. Identify channels used strictly for automated interlocks (e.g., hardwired turbine trip relays) that do not require independent faceplates: count = N_Pure (0 POs).
c. Identify channels requiring operator faceplates, historical archiving, or WinCC alarms: count = N_Visualized.
Calculate S7 F Systems Software Licenses:
a. For a redundant CPU 410-5H pair, allocate 2x S7 F Systems Runtime Licenses.
b. On the Engineering Station, ensure 1x S7 F Systems Engineering License is installed in Automation License Manager (ALM).
Calculate AS Process Objects and Size CPU 410 SEC Cards:
a. Total AS POs = N_Visualized (e.g., if 250 signals use MonDiL and 50 motors use MotL, Total AS POs = 300 POs).
b. Select CPU 410 System Expansion Cards: For 300 POs, procure 2x System Expansion Card 500 POs (one SEC per CPU).
c. Insert the identical SEC cards into the rear slots of CPU 0 and CPU 1.
Calculate WinCC OS Runtime Licenses:
a. Total OS POs = Total AS POs (300 POs).
b. For an OS Single Station, select the nearest standard commercial license tier: e.g., SIMATIC PCS 7 OS Software Single Station V9.0 (500 PO).
c. In ALM, transfer the OS RT PO license key to the OS Single Station PC.
Verify License Accounting in SIMATIC Manager:
a. In SIMATIC Manager, select the AS project and execute Options -> Process Objects -> Total Process Objects.
b. Confirm that the counted PO consumption matches your visualized block total, verifying 0 POs consumed by F-channel blocks.

Verification

In SIMATIC Manager, open Options -> Process Objects -> Total Process Objects: verify that the reported AS PO count equals the number of instantiated APL blocks, with 0 POs charged for F_CH_DI/F_CH_DO.
In HW Config online, open CPU Module Information -> 'System Expansion Card': confirm that both CPUs display matching authorized PO capacity (e.g., 500 PO).
In Automation License Manager on the OS Single Station, run 'License Key -> Check': confirm all OS RT PO licenses display green status.

Limitations and Operational Precautions

Never treat I/O channel counts as PO license counts; doing so leads to severe over-licensing and inflated procurement costs. Conversely, failing to license the second CPU in a redundant H-station will trigger ALM licensing violation alarms.

Engineer FAQ

Do fail-safe channel driver blocks consume Process Objects in PCS 7?

No. Standard F-channel drivers (F_CH_DI, F_CH_DO, F_CH_AI) and safety logic blocks consume zero AS RT POs.

Why are two S7 F Systems RT licenses required for a redundant CPU 410H?

Because S7 F Systems licensing is charged per active central processing unit. In a redundant pair, both CPUs execute the safety operating system, requiring two runtime licenses.

What happens if the two SEC cards on a CPU 410H pair have different PO capacities?

The redundant CPUs will fail to synchronize and will reject entering RUN-Redundant mode until both CPUs have identical SEC cards.

How many POs does a MonDiL block consume?

One AS RT PO in the controller and one OS RT PO in WinCC.

Can I upgrade CPU 410 SEC capacity later without replacing hardware?

Yes. Siemens offers SEC PO upgrade packages that can be loaded electronically onto the SEC cards via Automation License Manager without physical hardware swaps.